Recurring characters can become a lazy man's way of cranking out novels.

Or it can be an ambitious and ingenious exercise in building a world we wish to return to again and again, with a cast of characters we come to know and love.

There's nothing inherently wrong with series. They can be done well, or they can be done as a sad money grab. Sometimes a given series can be both, when an author doesn't know when to quit.

You use the phrase "from my vantage point as a reader" - when I am reading for pleasure, this is all that matters. I care not about the publisher's motives, the author's desires or a literature professor's opinions - I only care that I enjoy the experience.